两种常应力三轴排水剪模式下饱和黄土失稳特征试验

Test on Instability Characteristics of Saturated Loess Under Two Constant-Stress Triaxial Drained Shear Modes

摘要

为探究两种孔压模式下饱和重塑黄土的强度衰减规律和剪切变形规律,本文开展了增加孔压常应力排水剪切(CQD)试验和减小围压常应力排水剪切(RPD)试验,并提出了应变速率增量法判断黄土试样的失稳点.结果表明:在CQD试验中,孔压增速升高时试样更容易失稳;在RPD试验中,围压减小越快,试样失稳越早,且初始固结压力及初始孔隙比对两种加载模式下试样的失稳时间均有影响.对于初始状态(孔隙比、围压)相近的饱和黄土试样,RPD试样在失稳时的平均有效应力更高,且失稳时间更早;试样失稳至剪切结束,RPD试样的有效主应力降低幅度约为CQD试样的2倍.在CQD试验中,受局部超孔压累积影响,黄土试样的有效应力仅在局部范围内降低;而在RPD试验中,受静孔压影响,饱和黄土试样的整体有效应力降低,较前者更易发生失稳.

Abstract

Rainfall infiltration and groundwater level fluctuations are important factors to induce loess slope instability. In this paper, triaxial drained shear tests were conducted under two constant stress modes with increasing pore pressure (CQD) or decreasing confining pressure (RPD), the strength attenuation and shear deformation of saturated remolded loess under two pore pressure models were studied. The incremental strain rate method was proposed to identify the instability point of loess samples. The test results show that: In the CQD test, when the pore pressure growth rate of the sample increases, it is more prone to instability; In the RPD test, when the confining pressure of the sample decreases faster, the instability occurs earlier, and the initial consolidation pressure and initial void ratio have influence on the occurrence of instability in the sample under the two loading modes. For saturated loess samples with similar initial state (void ratio and confining pressure), the mean effective stress is higher at the instability point in the RPD sample and the occurrence of instability is also earlier. During the process of instability to the end of test, the reduction of effective principal stress in the RPD sample was found about twice that of the CQD sample. It can be inferred that in the CQD test, the reduction of effective stress of the loess sample is in a local range due to the accumulation of local excess pore pressure, while in the RPD test, the overall effective stress of the saturated loess sample decreases due to the influence of static pore pressure, and it is more prone to instability than in the CQD case.

关键词

常应力排水剪切 / 黄土 / 孔压发展规律 / 失稳 / 有效应力

Key words

constant stress drained shear / loess / pore pressure development law / instability / effective stress

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基金资助

国机集团科研专项(ZDZX202504)

国机集团科研专项(CMEC24FN01)

陕西省创新能力支撑计划项目(2024RSCXTD49)

陕西省创新能力支撑计划项目(2023CXPT46)

国机集团青年基金重点项目(QNJJZD202217)

国家自然科学基金项目(42041006)